Thursday, December 15, 2011

Multitouch patches posted

After pulling way too many 12+ hour days, I've finally polished the patchset for native multitouch support in the X.Org server into a reasonable state. The full set of patches is now on the list. And I'm still expecting this to get merged for 1.12 (and thus in time for Fedora 17).

The code is available from the multitouch branches of the following repositories:

Below is a short summary of what multitouch in X actually means, but one thing is important: being the windowing system, X provides multitouch support. That does not mean that every X application now supports multitouch, it merely means that they can now use multitouch if they want to. That also includes gestures, they need application support.

A car analogy: X provides a new road, the applications still have to opt to drive on it.

Multitouch events

XI 2.2 adds three main event types: XI_TouchBegin, XI_TouchUpdate and XI_TouchEnd. These three make up a touch sequence. X clients must subscribe to all three events at once and will then receive the events as they come in from the device (more or less, grabs can interfere here). Each touch event has a unique touch ID so clients can track the touches over time.

We support two device types: XIDirectDevice includes tablets and touchscreens where the events are delivered to the position the touch occurs at. XIDependentDevice includes multitouch-capable touchpads. Such devices still control a normal pointer by default, but for multi-finger gestures are possible. For such devices, the touchpoints are delivered to the window underneath the pointer.

That is pretty much the gist of it. I'll post more information over time as the release gets closer, so stay tuned.

Pointer emulation

Multitouch can be a compelling interaction method but as said above, X only provides support for multitouch. It will take a while for applications to pick it up (Carlos Garnacho is working on GTK3) and some never will. Since we still need to interact with those applications, we provide backwards-compatible pointer emulation. Again, the details are in the protocol but the gist of it is that for the first touchpoint we emulate pointer events.

That's the really nasty bit, because you now have to sync up the grab event semantics of the core, XI 1.x and XI2 protocols and wrap it all around the new grab semantics. So that if you have a multitouch app running under a window manager without multitouch support everything still works as expected.
That framework is now in place too though I expect it to still have bugs, especially in the hairier corner cases.

But other than that, it should work just as intended. I can interact with my GNOME3 desktop quite well and I get multitouch events to my test applications.